The popup could definitely be a little less "sales-pitch-y", but to be fair to Avast, they do need to advertise the paid product. Man can not live by empty electrons alone.
To the nuts and bolts of it.
Support for 4.8 will end around the end of the year, in all likelihood. So prior to that happening, you need to update your free version. Or purchase the updated pro or security suite version, if you wish to. Or migrate to a different AV.
Of those three options, I chose to update my free version to the latest, and its' working like a honey. I suggest you do the same. Follow the prompts to update to the latest free version.
Most users don't have tech problems in doing this, but occasionally some do, and in those cases, a full removal, restart, a running of the Uninstall Utility
, restart, and re-installation of the new version usually fixes any problems.
Any removal/installation of an antivirus is best done offline, as the computer is unprotected during the time the AV is removed.